Glycerol carbonate synthesis via Zn(OBu)2/AlCl2(OBu) initiated-glycerolysis of urea

Abstract

Glycerol carbonate (4-hydroxymethyl-1,3-dioxolane-2-one) was efficiently synthesized from glycerolysis of urea initiated by Zn(OBu)2/Al(OBu)Cl2. The zinc-aluminum complex mixture was prepared from zinc chloride (ZnCl2) and aluminum tri-sec-butylate (Al(OBu)3. The complex successfully initiated the urea glycerolysis in 1 : 1 ​mol ratio of glycerol to urea to produce glycerol carbonate up to 85% and selectivity up to 97% at 150 ​°C and 1 ​atm of N2 for 4 ​h in the absence of solvents. Isocyanate was observed as a key intermediate in this reaction. A kinetic study showed the reaction likely followed pseudo first-order kinetics with estimated activation energy (Ea) of 38 ​kJ/mol. Density-functional theory calculations with MN15-L functional described the formation of glycerol carbonate as spontaneous with the Gibbs free energy of −28.41 ​kJ ​mol−1.